Propeller blade



Dec; 23 1941' F- GEHRET f 2,266,858

I v PROPELLER BLADE oigvn'al Filed May 2e, 1938 2 sheds-sheet 2 extending chordwise between Patented Dec. 23, 1941 rnorELLEn BLADE t Edward Fayette Gehre't, Cleveland, Ohio, assignor to. Aviation Manufacturing Corporation,

Chicago, Ill.

original application May 2c. 193s, serial No.

Divided and this application June 12,

1939, Serial No. 278,590 l 2 Claims.'

The invention relates to hollow steel propeller blades for airplanes.

' In practice, it has been found .that when a hollow steel propeller blade lis formed .from a' straight cylindrical blank with a seamless leading edge which is straight and parallel to the lar blank'from which the blade is made. Fig.` 21sv axis of the blank throughoutits working length,

andthe curved trailing edge is formed by welding face-sections together, the planform is such that the blade is aerodynamically inelcient and unstable due to the fact that the center of air pressure at substantially all cross-sections is gitdcoincident with the longitudinal axis of the The present invention contemplates producing a hollow steel propeller blade from a seamless metal blank, bending the tufiular portion usedv Theinvention consists in the several novel features which are hereinafter set forth and are more particularly dehned by claims at the conclusion hereof. In the drawings: Fig. 1 is a plan ofthe tubua section of the blank after it has been swaged `and upset to form a shank on the blank.- Fig. 3

is a plan illustrating the bending of the portion of the swaged blank which is used'for forming the foils so as to provide a contour along one side thereof which conforms to the desired contour of the leading'edge while said portion of for forming'the faces longitudinally, shaping the blank to form a longitudinally curved seamless leading edge, and a trailing edge and tip by trimming and welding the blank. This makes it possible to provide any desired contour at the leading and trailing edges so that the air-loading in night will produce substantially no twisting or result in instability of utterf and to locate the center of air pressure at all cross-sections of the blade substantially coincident with the longitudinal center of the blade, so that the blade will have maximum aerodynamic efficiency.

One object of the invention is to provide hollow steel propeller blade formed pf a tubular Ablank and forming the blade with a ycurved seamless leadingA edge and a trailing edge by Joining marginal portions of the faces so the blade will be aerodynamically efficient.

Another object of the invention is to provide a hollow steel propeller blade having a seamless edge and tip formed by a weld between the facesections, the proportions being of such contour that twistingor flutter will be prevented, the center of pressure of each section being coincident with the axis of the blade at substantially all cross-sections.

Another object of the invention to provide the blank remains tubular and so that the blank may be folded upon itself along that line to form a seamless leading edge. Fig. 4- is an outer end view of the bent blank shown in Fig. 3. Fig. 5 isa longitudinal section illustratingthe manner of attening the tubular blank after it has been bent as aforesaid. Fig. 6 is a section on line 6 -6 of Fig. 5. Fig. 7 is a plan illustrating the blank after it has been attened and after the face sections have Ibeen embossed to for'm integral `raised portions in said faces. vertical longitudinal section illustrating the manner of embossing the facesections between dies to form raised portions on the faces. Fig. 9

.is a section on line 9--9 of Fig. 7. Fig. 10 is a sectionA on line Ill-lll of Fig. 8. Fig. 11 is a section of the blank after the outer faces of the face sections have been milled off to provide reduced wall-thickness in the central portions pi the face sections and greater thickness at the leading edge between its faces, and a trailing p tipi? Fig. 16 is a section illustrating the dies in l seamless leading edge and the trailingA edge. Fig. 12 is a plan of the blank after it has been. trimmed tothe contour desired-for the trailing edge and tip. Fig. 13 is a section on line I3-I3 of Fig. 12. Fig. 14 is a section on lineM-Ilof Fig. 12. Fig. 15 is a view illustrating the manner of welding together th'e separate face-sections to form the trailing edge of the blade and which'the-Iace-sections are expanded to form a hollow steel propeller blade, having integral shank and face-portions, a seamless leading edge, a trailing edge formed by joining the face-sections. the wall-thickness at the leading edge `being greater than the wall-thickness' at the trailing edge, and wall-thickness in the face-portions the edges, less than that at both edges.

Other objects of the invention will appear from the detailed description.

the camber and suction membersl of the blade.

Fig. 17 isa transverse section of the finished blade.

Incarryin'g out the invention, a tubular'blanlrY I a of mild carbon steel and of uniformA diameter, y'

after its interior hasbeen polished and itsexterior turned to size, as shown in Fig. 1, is swaged and upset, in axial direction adjacent one of its ends to provide a shank a1 of increased wall-thickness and decreased exterior diameter, for attachment to a propeller hub, and a portion a2 of gradually increasing diameterand decreasing wall-thickness, as shown in Fig. 2, the outer portion a3 being left unchanged in diameter and wall-thickness.

Next, the blank is heated and the tubular portion a3 is bent between suitable dies b, so that it will be curved, as as b4, andits axis will be curved, as indicated by the line b1. The bend is made ori-a suitable radius so that the side having the greater radius will be curved substantially to the desired contour of the leading edge of the blade'. The bending of the tubular -portion a3 in this manner is of importance in forming aseamless leading edge for the blade or without interruption or cutting of the wall of the blank and in providing a contour of the leading edge K which is aerodynamically eiiclent.

After the blank has been bent, as shown in Fig. 3, the tubular portion a3 is heated and flattened between dies c, as illustrated in Figs. and 6. This attening is done by pressure perpendicular to the plane of the bend to shape the bent tubular portion a3 into flat faces which are substantially parallel to the plane in which the portion l)4 has been bent, and are joined together by semicircular curves a4, a5; 'I'he curved connecting portion a4 between the faces will correspond in curvature on the arc of greater diameter formed during the bending operation illustrated in Fig. 3, and will conform to the desired leading edge contour. The connecting'bend a5 at the other `side of the flattened blank will be disposed at the curved portion of the blank bent on the lesser radius. The contour of the latter portion is unimportant because it is subsequently cut away informing the trailing edge of the blade.

Next, a former d is inserted into the flattened blank through its outer end for embossing the attened faces of the blank. The blank with the former therein is then placed between dies e which have mating cavities e1, e2 conforming in contour to the former d. The side edge d1 of this former conforms approximately to the contour of the folded edge-a4 of the blank usedfor forming the leading edge of the blade to a point adjacent the outer end of the blank and its other side edge d2 is disposed inwardly of the fold a5 at the other side of the blank.

'I'he cavities el, e2 in the dies conform to the contour of the former d and are adapted to emboss the faces outwardly on a line slightly outwardly of, and conforming to, the contour of the former. When the dies are brought together` the face-portions surrounding the former will be forced closely together and form raised or embossed portions on each of the faces on the .line indicated at a6. The embossed portion adja-z tip-end and the die cavities are correspondingly tapered so that the embossed portions of the faces of the blank will diverge slightly from their inner ends toward their outer ends. The bottoms of eachof the Idie cavities e1, e2 are parallel to the faces of formed d and are of slightly greater depth adjacent the fold a4 of the blank than at the opposite edges, so that when the dies are brought together the face-portions of dies e will force the portions of the blank adjacent the fold a* somewhat closer together than the-portions ofthe die-faces at the opposite edge will force together than the portions adjacent the fold a5,

the milling cuts will leave practically full wallthickness around and adjacent the portion a4 which is used for forming the leading edge; the portions around and adjacent the fold a.5 will have a lesser Wall-thickness, and the intermediate portions a'I of the face-sections, where the embossed portions have been removed, will have a wall-thickness less than that adjacent both bends a4, a5. The thickness of the metal forming the leading and trailing edges may be varied by the depth of the milling cut as well as the heighth of the embossed portions and the relative wallthickness of the portions adjacent the bends a4., a.5 may be varied by varying the relative depth of the bends around the embossed portions. By using a form d having its thickness longitudinally tapered from its outer towards its inner end and together the portions of the blank adjacent the fold a, for a purpose presently to be described.

making parallel mill cuts, the face-sections are given a gradually decreasing wall-thickness towards the tip of the blade.

This embossing and slab mill cutting results in forming the blank with a zone of maximum wallthickness across and along the leading edge, a zone of somewhat thinner wall-thickness along the trailing edge, and zones of minimum wallthickness intermediate the marginal portions of the faces for correct distribution of the metal for aerodynamic efficiency and lightness.

Next, the blank is cut off or sawed through both of the face-sections on the line indicated by f in Fig. 7, so that the blank will have the planform illustrated in Fig. l2. When so cut, the former d will be removed. The cut extends from a point as close as possible to the tip on the leading edge around the tip and conformably to the trailing edge to the shank.

The inner faces'of the face-sections along the trailing edge and around the tip are next welded together as at g by resistance welding under pressure, as illustrated in Fig. 15.

Next, the blank is placed between dies h which have cavities of a contour conforming to the desired shapes of camber and pressure faces of the blade. While held in dies h the faces are expanded while heated, by fluid under pressure internally applied to`the blank, to conform to the die cavities, so the outer surfaces of the faces :lill have the desired suction and pressure conour.-

Next, the edges of the blade are trimmed or ground and polished, as desired, to form a smooth leading and trailing edge.

'I'his application is a division of the application illed by me on May 26, 1938,'for Letters Patent No. 2,192,008, granted February 27, 1940. I

The invention exemplifies a blade having an integral shank and face-sections with a jointless leading edge which is curved for maximum aerodynamic efliciencyand a tip and trailing edge formed by welding and in which the blades are 'shaped for maximum aerodynamic efliciency.

The invention is not to be understood as re-5 stricted tothe details set forth, since these may be modied within the scope of the appended claims, without departing from .the spirit and scope of the invention.y

Having thus described the invention, what I claiin as new and desire to secure by Letters reduced wall-thickness decreasing in thickness l0 from the root toward the tip, and the wall around the seamless leading edge being thicker than the face-walls adjacent the trailing edge.

2. A one-piece hollow kmetal propeller blade comprising a tubular shank, camber and pressure faces, a seamless leading edge, longitudinally curved substantially throughout its working 5 length and to the tip and consisting of metal bent longitudinally and curved transversely and a longitudinally curved trailing edge consisting of face-portions autogenously welded together, the metal around the seamless edge and the trailing edge being thicker than the combined thickness of the middle portions of the faces. 

